Introduction
Avian Influenza (AI) outbreaks can be devastating for the poultry industry and result in enormous financial losses. Biosecurity is essential to control the disease, but airborne transmission through the air inlets can expose farms despite the highest biosecurity measures. Airborne transmission of AI is still controversial and not well understood. In the 2015 outbreak in the US, it was observed that bird mortality mainly occurred near the inlets of the infected farms (Zhao et al., 2019). The virus could attach to fine dust particles to travel through the air.
Spekreijse et al. (2012) investigated dust-borne transmission of AI by inoculating white leghorn chickens with the AI virus and evaluating infection in non-inoculated chickens in a nearby room. Infection of non-inoculated birds was observed in two of the four experiments. The authors showed that airborne transmission was 20-fold less successful than contact infection among birds that shared the same room. In another experiment with similar settings (Spekreijse et al., 2011), the amount of virus present in the air was low even when there was a great viral shedding by the inoculated birds. The authors concluded that, depending on the distance, AI infection caused by airborne transmission is unlikely to happen.
Torremorell et al. (2016) collected air samples from inside and outside (5m, 70-150m, 500-1000m) turkey and layer facilities positive for Highly Pathogenic Avian Influenza (HPAI). The authors found that 45% of the air samples were positive at a 5m distance, 3.5% were positive between 70 to 150 m and no positive air samples were obtained at 500 to 1000m. This result indicates the presence of the AI virus in the air outside infected poultry houses. However, the infection of other birds with the airborne virus depends on the amount of viable virus inhaled (Ssematimba et al., 2012). Therefore, the actual probability of disease is uncertain.
Incoming air filtration has been studied as a way to prevent dust entrance and airborne diseases in swine and poultry (Dee et al., 2006; Dee et al., 2009; Dee et al., 2010; Kamiyama et al., 2011; Wenke et al., 2017; Wenke et al., 2018; Zhao et al., 2018). Although previous research showed that HEPA filters are one of the most effective in retaining dust (99.97% retention of particles ≥0.3 μm) and reducing the airborne spread of diseases (Dee et al., 2006), these filters can be expensive and hard to adapt to different ventilation systems in poultry barns.
One alternative to this problem could be to use less efficient filters in conjunction with another preventative measure. Kamiyama et al. (2011) evaluated the effectiveness of different filters on AI prevention. They found that a nonwoven fabric impregnated with ostrich antibodies against the hemagglutinin of the H5N1 virus effectively prevented AI airborne transmission.
Woven geotextile fabric was previously used over the exhaust fans to prevent the exit of particulate matter from a broiler facility (Jerez et al., 2013). It was found that the system used in this research effectively reduced the emission of particulate matter with ≤10µm in diameter.
Landscape fabric is affordable and available. Therefore, the objective of this research was to test the outcomes (pros or cons) of using landscape fabric as air inlet covering to prevent/reduce dust entry (and potentially pathogens) into poultry barns.
It was hypothesized that using landscape fabric on the air inlets can reduce the airspeed, increase differential pressure around the fabric (filter), and change the air pattern in the barn.
Question
What would be the outcomes (pros or cons) of using landscape fabric as ventilation covering to prevent/reduce dust and pathogen entry into poultry barns?
Report on a pilot study
Location of the study
Poultry Research Centre, University of Alberta
Dimension of the barn
The dimensions of the barn used as the experimental house in this study were 48.5 feet × 29.8 feet × 9.75 feet, Length × Width × Height.
Barn ventilation system
The house uses a negative pressure ventilation system. There are two air inlets mounted on the ceiling. The inlets are equipped with hoods from the outside and eaves from the inside (Figure 1). Honeycomb light traps are used on air inlets and fans (Figure 2). The house has four exhaust fans (two on the north side wall and two on the south side wall). The fans were set to the maximum speed (1060 RPM) and the air inlet openings were set to the maximum opening before starting the experiment. Fan speed was kept consistent over the course of the experiment.
Filters and treatments
There were three ventilation treatments in this study: Control with no filter, and two types of landscape fabrics to cover the air inlets:
- Weed Barrier Fabric, Pro Black (3.0 oz)
- DeWitt PRO 5 Weed-Barrier (5 oz). Woven Landscape Fabric
The fabrics were cut and installed on the air inlet hoods using industrial duct tape (Figure 3).
Measurements
The differential static pressure across the inlets was measured using a digital manometer (DJDK model SW‑512C, Figure 4a). The manometer was connected to the outside and inside (underneath each air inlet) via vinyl tubes and a static pressure probe.
The airspeed was measured using an anemometer (Kestrel 3500 Weather Meter, Figure 4b), mounted on a tripod at 12 different locations (two sides of each air inlet’s openings, four locations in the middle of the house halfway between the air inlet and fans, and in front of four fans). The average airspeed was calculated for each ventilation scenario (the control, 3 oz fabric, and 5 oz fabric).
A smoke test was conducted for each ventilation scenario (the control, 3 oz fabric, and 5 oz fabric) using wire pull smoke grenades to visualize the airflow pattern and the smoke clearance time by the fans. The smoke clearance time was measured visually and subjectively.
Results and discussion
The results of static pressure are shown in Figure 5. Using the 3 oz landscape fabric on air inlets increased the static pressure by 70%, 120%, and 84% over the three days. The higher increase in the static pressure on the second day might be related to the rainy weather that wet the fabric. Using the 5 oz landscape fabric increased the static pressure by 164% and 120% over the three days. The optimal static pressure depends on various factors, including inlet design and placement, inlet opening size, inside/outside temperature difference, and house width. The optimal static pressure in poultry barns ranges between 0.04 to 0.15 inches of water (10 to 37 Pa) to achieve the required air throw requirements. Static pressure above 0.20 inches of water (50 Pa) should be avoided. Using different landscape fabrics (3 oz and 5 oz) in the current pilot study created static pressure above 0.20 inches of water (Figure 5).
Figure 6 illustrates the effects of using the landscape fabrics on the airspeed in the barn. Using the 3 oz and 5 oz landscape fabrics reduced the airspeed by 67% and 73%, respectively compared to the control treatment.
The effects of using landscape fabrics on the smoke clearance time are shown in Figure 7. It took 3.5, 9.5, and 12.5 minutes for the smoke to be cleared by the fans in the control, 3 oz fabric, and 5 oz fabric ventilation scenarios, respectively. No differences in the airflow pattern among the different ventilation scenarios (control, 3 oz fabric, and 5 oz fabric) were observed.
The results of the current pilot study indicated that using a 3 oz or 5 oz landscape fabric affected the research barn ventilation negatively under the experimental conditions. However, running the trial in a commercial setting with a different ventilation system (cross-ventilation, tunnel ventilation, etc.) seems necessary to answer the research question precisely.
Report on a commercial farm study
Location of the study
The study was conducted on the lower floor of an old double-decker broiler barn in the Edmonton region. The barn is a representative of a large number of old and small barns, which have been considered risky barns in terms of avian influenza outbreaks. We assumed these kinds of barns do not hold the pressure the same way new ones do because they can leak like sieves in some cases, and they have old ventilation systems that cannot cope with being hindered by reduced airflow from covered inlets.
Barn ventilation system
The barn uses a cross-ventilation system. The barn has a continuous air inlet at the top of the wall and 12 individual wall inlets to add capacity in summer and to cover off winter ventilation (Figure 8). The house has five exhaust fans (Figure 9). The fans were set to the maximum speed and the air inlet openings were set to the maximum opening before starting the experiment. Fans’ speed was kept consistent over the course of the experiment.
Filters and treatments
A 3 oz or 5 oz landscape fabric was used in the pilot study, which resulted in a significant drop in ventilation efficiency. Given the results of the pilot study, a decision was made to use a 2 oz fabric to assess the drop in ventilation efficiency. There were two ventilation treatments in this study: Control with no filter, and 2 oz landscape fabric as a ventilation cover. The fabric was mounted on the individual and continuous inlets (Figure 10) using industrial duct tape (Gorilla Tough and Wide Black Tape 25YD). Given that our trial was to test the effects of the fabric on ventilation efficiency in the short term, duct tape did the job, but it may not last for a longer time. If the fabric is supposed to remain on inlets for longer-term during the AI outbreak, you might consider using Velcro strips to attach the fabric. Alternatively, depending on the inlet type, you could consider building a wooden frame to attach the fabric to inlets. We have not assessed the later installation ideas, and there is still work to be done to assess the best application method.
Measurements
The differential static pressure was measured using a digital manometer (DJDK model SW‑512C, Figure 4a). The manometer was connected to the outside and inside of the house via vinyl tubes and a static pressure probe.
The airspeed was measured using an anemometer (Kestrel 3500 Weather Meter, Figure 4b), mounted on a tripod at five different locations across the house. The average airspeed was calculated for each ventilation scenario (the control and 2 oz landscape fabric). All measurements were conducted in one day.
Results and discussion
The effect of using a 2 oz landscape fabric on static pressure is shown in Figure 11. Using the 2 oz landscape fabric on air inlets increased the static pressure by 34% compared to the control treatment. The static pressure was 0.09 and 0.12 inches of water for the control and 2 oz fabric, respectively (Figure 11). As mentioned previously, the optimal static pressure in poultry barns ranges between 0.04 to 0.15 inches of water (10 to 37 Pa) to achieve the required air throw requirements. Using a 2 oz landscape fabric under the commercial barn condition did not deteriorate the static pressure.
Figure 12 illustrates the effects of using 2 oz landscape fabric on the airspeed in the barn. Using the 2 oz fabric reduced the airspeed by 20% compared to the control treatment (Figure 12).
The results of the commercial barn study indicated that using the 2 oz landscape fabric on air inlets did not affect the ventilation efficiency significantly under the experimental condition. It should be emphasized that the commercial barn had an old structure and was not as tight as a modern barn. Thus, the results of the current commercial barn study should be used cautiously in other barns.
References
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